Conventionally, micro-machine members produced from a wafer made of monocrystal silicon through semiconductor processes can be processed by a micrometer order, and thus a wide variety of micro-functional devices haven been realized using the same. Particularly, optical deflectors in which a reflection surface is torsionally oscillated by means of an oscillator device formed by such technique to perform optical scanning, have the following advantageous features as compared with an optical scanning optical system using a rotary polygonal mirror such as a polygon mirror. That is, the optical deflector can be made small in size, and the electric power consumption is slow. Particularly, when it is driven at a frequency around the natural oscillation mode of torsional oscillation of the oscillator device, the power consumption can be made low.
U.S. Pat. No. 7,061,063 discloses a technique for forming a torsion spring of an X-letter shape by performing anisotropic etching to a Si wafer as well as a technique for applying an optical deflector comprising a torsion spring of X-letter shape to an image forming apparatus.